Mind Time: The temporal factor in consciousness by Benjamin Libet, Harvard University Press, 拢19.95/$29.95, ISBN 0674013204
CAN neuroscientists say anything interesting about consciousness? Judging by the stream of books and conferences on the topic, you can safely assume they believe they can. What makes Benjamin Libet different from all the others writing on the subject, though, is that he has actually spent the past 40 years experimenting on the topic. His findings have played a central role in others鈥� speculations. Now he has put his life鈥檚 work into a single short book.
The core of Libet鈥檚 findings can be simply summarised. If I sit on the edge of my bed and decide to wiggle my toes, the brain processes necessary for the wiggling to occur begin about half a second before I am aware that I have made the decision. Libet finds this troubling; if the brain processes precede my sense of having made a decision, what part does my conscious decision making play? Who indeed is the 鈥渕e鈥� that does the 鈥渄eciding鈥�?
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In reality, you don鈥檛 need Libet鈥檚 experiments to tell you that much of what we do precedes conscious awareness. To play their strokes, tennis players and cricketers must adjust the racket or bat to the oncoming ball far faster than would be possible if they had to make a conscious decision each time on how to play a shot 鈥� indeed, if they had to wait that long they would inevitably fail to make contact at all.
Libet finds this paradoxical. To 鈥渟ave鈥� consciousness and avoid the Cartesian error of assuming that there is some separate mind-stuff out there, he suggests that what conscious decision making can do is to exert a veto over the unconscious brain processes; in the half-second available to me I can refuse to wiggle my toes. He proposes that we can do this because we possess something he calls a 鈥渃onscious mental-field鈥�, perhaps reflected in the current flows across the brain that can be detected by electroencephalography.
I find this a non-solution to a non-problem. It is only because he naively equates consciousness with awareness, and insists that it must be embedded in the brain and not in the broader wisdom of the body, that he becomes trapped in a philosophical minefield, rather than a mental-field, of his own making. But then if he weren鈥檛 naive, he probably wouldn鈥檛 have done his experiments in the first place, and neuroscientists would have been even freer to speculate beyond their remit.